Kaplan + Sadock's Synopsis of Psychiatry, 11e

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Chapter 5: Examination and Diagnosis of the Psychiatric Patient

Any evaluation of dementia should consider medication effects, metabolic derangements, infections, and nutritional causes that may not produce abnormalities on neuroimaging.

Indications for Neuroimaging in Clinical Research

Analysis of Clinically Defined Groups of Patients.  Psychiatric research aims to categorize patients with psychiat- ric disorders to facilitate the discovery of neuroanatomical and neurochemical bases of mental illness. Researchers have used functional neuroimaging to study groups of patients with such psychiatric conditions as schizophrenia, affective disorders, and anxiety disorders, among others. In schizophrenia, for exam- ple, neuropathological volumetric analyses have suggested a loss of brain weight, specifically of gray matter. A paucity of axons and dendrites appears present in the cortex, and CT and MRI may show compensatory enlargement of the lateral and third ventricles. Specifically, the temporal lobes of persons with schizophrenia appear to lose the most volume relative to healthy persons. Recent studies have found that the left temporal lobe is generally more affected than the right. The frontal lobe may also have abnormalities, not in the volume of the lobe, but in the level of activity detected by functional neuroimaging. Persons with schizophrenia consistently exhibit decreased metabolic activity in the frontal lobes, especially during tasks that require the prefrontal cortex. As a group, patients with schizophrenia are also more likely to have an increase in ventricular size than are healthy controls. Disorders of mood and affect can also be associated with loss of brain volume and decreased metabolic activity in the frontal lobes. Inac- tivation of the left prefrontal cortex appears to depress mood; inactiva- tion of the right prefrontal cortex elevates it. Among anxiety disorders, studies of obsessive-compulsive disorder with conventional CT and MRI have shown either no specific abnormalities or a smaller caudate nucleus. Functional PET and SPECT studies suggest abnormalities in the corticolimbic, basal ganglial, and thalamic structures in the disorder. When patients are experiencing obsessive-compulsive disorder symp- toms, the orbital prefrontal cortex shows abnormal activity. A partial normalization of caudate glucose metabolism appears in patients taking medications such as fluoxetine (Prozac) or clomipramine (Anafranil) or undergoing behavior modification. Functional neuroimaging studies of persons with attention- deficit/hyperactivity disorder (ADHD) either have shown no abnormalities or have shown decreased volume of the right pre- frontal cortex and the right globus pallidus. In addition, whereas normally the right caudate nucleus is larger than the left caudate nucleus, persons with ADHD may have caudate nuclei of equal size. These findings suggest dysfunction of the right prefrontal- striatal pathway for control of attention. Analysis of Brain Activity during Performance of Specific Tasks.  Many original conceptions of different brain region functions emerged from observing deficits caused by local injuries, tumors, or strokes. Functional neuroimaging allows researchers to review and reassess classic teachings in the intact brain. Most work, to date, has been aimed at language and vision. Although many technical peculiarities and limita- tions of SPECT, PET, and functional MRI (fMRI) have been overcome, none of these techniques has demonstrated clear

Space-occupying lesions can cause dementia. Chronic subdural hematomas and cerebral contusions, caused by head trauma, can produce focal neurological deficits or may only produce dementia. Brain tumors can affect cognition in several ways. Skull-based meningiomas can compress the underlying cortex and impair its processing. Infiltrative glial cell tumors, such as astrocytoma or glioblastoma multiforme, can cut off communication between brain centers by interrupting white matter tracts. Tumors located near the ventricular system can obstruct the flow of CSF and gradually increase the intracranial pressure. Chronic infections, including neurosyphilis, cryptococcosis, tuberculosis, and Lyme disease, can cause symptoms of demen- tia and may produce a characteristic enhancement of the menin- ges, especially at the base of the brain. Serological studies are needed to complete the diagnosis. Human immunodeficiency virus (HIV) infection can cause dementia directly, in which case is seen a diffuse loss of brain volume, or it can allow proliferation of Creutzfeldt-Jakob virus to yield progressive multifocal leu- koencephalopathy, which affects white matter tracts and appears as increased white matter signal on MRI scans. Chronic demyelinating diseases, such as multiple sclerosis, can affect cognition because of white matter disruption. Mul- tiple sclerosis plaques are easily seen on MRI scans as periven- tricular patches of increased signal intensity. Figure 5.8-1 Brain slices. Top: Huntington disease. Atrophy of caudate nucleus and lentiform nuclei with dilatation of lateral ventricle. Bottom: Normal brain. (From Fahn S. Huntington disease. In: Rowland LP, ed. Merritt’s Textbook of Neurology. 10 th ed. Philadelphia: Lippin- cott Williams & Wilkins; 2000:659, with permission.)